A man died in Lake Del Valle in Livermore after entering the water to retrieve an oar that fell from his family's boat and being unable to resurface on Saturday afternoon, according to East Bay Regional Park District.

The situation began around 3:45 p.m. in a cove across the lake from the East Beach, outside of the guarded area, according to EBRPD Police Department Capt. Al Elzey.

"According to witnesses after jumping into the water, the man immediately began to struggle and then went underwater," Elzey said in a press release.

Family members flagged down EBRPD marine patrol officers within minutes, and the officers marked the area while district lifeguards responded from swim zones and dove underwater in search of the missing man, according to Elzey.

Divers searched the area over the course of nearly six hours before the man's body was recovered shortly before 9:30 p.m. Saturday, the captain said. The decedent was identified by the Alameda County Coroner's Office on Sunday as Daniel Nathan Cullison, 26, of San Jose, according to the Bay City News Service.